An x-ray laminography apparatus is a kind of X-ray tomography apparatus for taking tomographic images of an object. The X-ray laminography apparatus has important features, noted below by which it differs from other types of X-ray tomography apparatus. More particularly, in the X-ray laminography apparatus, an X-ray beam is irradiated in a direction which is oblique to an object to be measured, so that the X-ray beam transmitting through the object obliquely thereof is detected by a detection unit. During the tomography, the object and an X-ray detection image are rotated in synchronism with each other on a plane which intersects an X-ray irradiation axis and image processing for adding a plurality of rotation images obtained during the synchronous rotation is carried out, thereby making it possible to selectively obtain only an image on a tomographic plane extending at a specified depth inside of the object. The thus obtained image is a tomogram on the rotation plane including the intersection of the rotation axis of the object and the X-ray irradiation axis. A fundamental measuring method and its principle are described in U.S. Pat. No. 5,351,278 to Koshishiba et al and will not be detailed herein.
For example, the X-ray laminography apparatus is used either to observe only a specified layer inside a multilayer electronic circuit board to find defects or to non-destructively inspect an internal portion at a specified depth of electronic parts, mechanical parts or other matters which cannot be seen from the outside.
FIG. 8 diagrammatically shows the fundamental construction of the X-ray laminography apparatus. As shown in FIG. 8, an object 50 to be measured which is held on a rotary stage 16 having a rotation axis 13 inclined with respect to a radiation direction 4 of an X-ray beam is rotated and an X-ray image detected on a detection surface orthogonal to the rotation axis 13 is rotated: in synchronism with the rotation of the object 50 to belmeasured, so that a tomographic image on a rotary plane where a line 4 connecting an X-ray source 1 and the center of the detection surface intersects the rotation axis 13 can be obtained. Reference numeral 60 designates an xy-stage adapted to move the object 50 on a two-dimensional plane to change an X-ray irradiation area.
In the case of a conventional X-ray laminography apparatus, the xy-stage 60 is movable within a plane on the rotary stage 16 for positioning the object 50 to an observation position. The rotary stage 16 is rotatable endlessly, thus making it difficult to move the xy-stage 60 by driving it with a motor. The reason for this is that the motor and a mechanism for horizontally moving the stage are arranged on the xy-stage 60 and caused to rotate by the rotary stage 16 and so it is very difficult to supply electric power externally and continuously to the motor rotating along with the xy-stage 60. Inevitably, the xy-stage 60 used for moving the object 50 horizontally is moved horizontally so as to change the observation position of the object.
Therefore, when the observation position of the object 50 is desired to be changed, positioning of the object 50 must be carried out by getting the X-ray source turned off temporarily for preventing the operator from encountering radiation. For example, when observing an internal layer of a multilayer printed circuit board or an internal structure of electronic parts or mechanical parts, positioning is conducted without resort to visual reference to any X-ray transmission image and in fact, positioning to an intended observation position cannot be effected accurately within a short period of time.
Conceivably, a method may be proposed in which an xy-stage drive motor is arranged on the rotary stage 16 with the aim of remotely operating the xy-stage and electric power is supplied to the motor through slip rings and brush electrodes which are movable while being in contact to each other. In this proposal, however, disposition of the slip rings and brushes in a Central opening 70 of rotary shaft through which the X-ray beam passes must be avoided and they are required to be disposed at the outer periphery of the rotary shaft, raising problems that the sliding speed of the brushes becomes high to accelerate deterioration of the brushes and the apparatus as a whole becomes large and costly.
The conventional X-ray laminography technology is very excellently featured in that high-resolution tomographic images can be obtained on substantially real time base but nevertheless it has failed to contribute to widespread use of practical apparatus.
It is an object of the present invention to provide an X-ray tomography apparatus capable of positioning an object to be measured to a desired observation position while permitting an X-ray transmission image of the object for seeking an area of desired tomographic image and an X-ray tomography method using the apparatus.
A second object of the invention is to provide a compact, inexpensive and highly-reliable X-ray tomography apparatus capable of positioning an object to be measured to a desired observation position while permitting an X-ray transmission image of the object to be watched and an X-ray tomography method using the apparatus.
A method of taking tomograms inside an object with an X-ray tomography apparatus according to the present invention comprises the following procedures. More particularly, an X-ray beam is irradiated to the object. An X-ray beam transmitting through the object is detected and a transmission image of the object is generated on the basis of the detected X-ray beam. While watching the transmission image of the object, the object is moved by means of a moving mechanism coupled to a drive unit to change an X-ray irradiation area of the object and the object is stopped at a desired position. The moving mechanism is disconnected from the drive unit. The object being irradiated with the X-ray beam is rotated about a rotation axis which is inclined with respect to an irradiation axis of the X-rays beam. An X-ray beam transmitting through the object is detected, a detected image is rotated in synchronism with the rotation of the object to provide a rotation image, and an image on a tomographic plane in the object which includes an intersection of the rotation and irradiation axes is generated on the basis of the rotation image.
According to the invention, an X-ray tomography apparatus for taking tomograms inside an object comprises an X-ray source for irradiating an X-ray beam to the object, a moving mechanism for moving the object to change an X-ray irradiation area of the object, a rotating mechanism for rotating the object about a rotation axis which is inclined by a predetermined angle with respect to an irradiation axis of the X-ray beam, a control unit for controlling the moving mechanism to cause it to move the object to a designated position so as to change an X-ray irradiation area of the object when the rotating mechanism is stopping at a predetermined position, and an X-ray detection unit for detecting a transmission X-ray beam, rotating a detected image in synchronism with the rotation of the object to provide a rotation image of the object and converting the rotation image into an electric signal.
While observing a transmission image of the object on the monitor screen, an operator can remotely move the object through the medium of the moving mechanism to stop the object at a desired observation position. A tomographic image of the object is taken at the observation position. During a series of operations ranging over positioning of the object and tomography, the operator can perform remote control from a position distant from the tomography apparatus without interrupting irradiation of the X-ray beam and a desired tomogram can be taken accurately within a short period of time.
Besides, according to the invention, an X-ray tomography apparatus for taking tomograms inside an object comprises an X-ray source for irradiating an X-ray beam to the object, a stationary base, first, second and third motors fixed to the stationary base, a hollow shaft driven to rotate by the first motor and having an opening in the center of rotation, an x-stage base fixed to the hollow shaft, x-guide rails fixed on the x-stage base, an x-stage slidable on the guide rails, y-guide rails fixed on the x-stage, a y-stage slidable on the y-guide fails and carrying the object, an angular position sensor for detecting a rotation position of the x-stage base, a first bevel gear mounted to a rotary shaft of the second motor, an x-stage drive unit having a second bevel gear and operative to move the x-stage on the x-guide rails as the second bevel gear rotates, a third bevel gear mounted to a rotary shaft of the third motor, and a y-stage drive unit having a fourth bevel gear and operative to move the y-stage on the y-stage rails as the fourth bevel gear rotates, the y-stage drive unit being supported on the x-stage and the fourth bevel gear being always held at a fixed position on the x-stage regardless of the movement of the x-stage.
The X-ray tomography apparatus according to the invention further comprises a first actuator for moving the first bevel gear to bring it into engagement with the second bevel gear, a second actuator for moving the third bevel gear to bring it into engagement with the fourth bevel gear, a control unit responsive to detection of a predetermined rotation angle by the angular position sensor to stop the rotation of the first motor, control the first and second actuators to release engagement of the first bevel gear with the second bevel gear and bring the third bevel gear into engagement with the fourth bevel gear, and an X-ray detection unit for detecting an X-ray beam transmitting through the object and passing through the opening to provide a detection image, rotating the detection image in synchronism with the rotation of the object to provide a rotation image and generating a tomographic image from the rotation image.
According to the X-ray tomography apparatus according to the invention, since the second and third motors for driving the xy-stage are fixed to the stationary base and electric power can always be supplied externally regardless of movement of the rotary xy-stage without using any slip rings and brushes, the operator can perform remote control from a position distant from the tomography apparatus without interrupting irradiation of the X-ray beam during a series of operations ranging over positioning of the object and tomography and a desired tomogram can be taken accurately within a short period of time. Further, since the y-stage drive unit is supported on the x-stage and the fourth bevel gear for moving the y-stage is always held at a fixed position on the x-stage regardless of slide movement of the x-stage, operation for positioning the object can be effected smoothly. The X-ray tomography apparatus of the invention is not increased in size to have a mechanism capable of remotely controlling the xy-stage.
The present invention is in no way limited to embodiments to be described hereinafter in the present specification. Those skilled in the art can obtain the same effects by using different mechanisms and modification which can fulfil the function comparable to that of elements and mechanisms used in embodiments disclosed in the present specification.